Physics Athens 2016

Charged Particle Equilibrium

Charged particle equilibrium (CPE) exists if for each charged particle with energy E leaving a volume V , there is an identical particle with same energy E entering V

A B C

• only a fraction of electron track deposits energy in voxel A → dose is low • in voxel B , a new electron starts but there is also part of electron track which started upstream in voxel A → dose is higher B • kinetic energies leaving voxel C is balanced by kinetic energies entering in this volume → equilibrium is reached at C

at C → Dose ≈ KERMA

kV Xrays

Lecture 24 MP 501 Kissick 2012